Interaction of generalist grasshoppers with native and exotic grasses: behavioral and molecular approaches

Generalist insect herbivores, such as grasshoppers, may either avoid feeding on exotic plants, thus enabling these plants to become invasive in the introduced range, or insects may incorporate exotic plants into their diet; this can contribute to the biotic resistance of native communities that potentially may prevent plant invasions. Although there has been some investigation of grasshopper feeding on native versus exotic plants, the results from these studies are inconsistent and consequently, the feeding preferences of grasshoppers are still poorly understood, especially on grasses. To address this issue, we combined behavioral and molecular approaches to accurately compare food consumption of the polyphagous red-legged grasshopper, Melanoplus femurrubrum, on native (Andropogon gerardii and Bouteloua curtipendula) and exotic, potentially invasive grasses (Miscanthus sinensis and Bothriochloa ischaemum). We found that M. femurrubrum grasshoppers demonstrated strong feeding preferences toward exotic grasses in experiments with intact plants under both field and greenhouse conditions, but they showed no preference in experiments with clipped leaves. Additionally, we sampled the gut contents of M. femurrubrum collected in the field and identified the ingested plant species based on DNA sequences for the noncoding region of the chloroplast trnL (UAA) gene. We found that exotic plants were prevalent in the gut contents of grasshoppers collected at both study sites in Ohio and Maryland. These results suggest that M. femurrubrum does not avoid feeding on exotic grasses which do not share coevolutionary history and can potentially provide biotic resistance should these grasses escape cultivation and become invasive in the introduced range.